1. Field of the Invention
The present invention relates to a liquid material supplier for causing a liquid material, such as ink, to be held in a uniform thin layer on a surface of a liquid material holding member, such as a roller or belt, and to an image forming apparatus having the liquid material supplier incorporated therein.
2. Description of Related Art
A printer, an image forming apparatus, or the like using a liquid material such as a liquid ink is so constructed as to form the liquid ink adhering to a rotating roller as a liquid material holding member into a uniform thin layer by using a regulating blade, transfer the thin layer onto a form plate or an image carrying member, and then scrape the ink remaining on the rotating roller therefrom by using a removing blade.
FIG. 10 shows a conventional ink supplier 2 using such a removing blade. The ink supplier 2 comprises a container 4 for containing ink 6. The ink 6 is supplied from an ink cartridge 8 to the container 4. In the upper part of the container 4, a roller 14 which rotates around a shaft 10 extending perpendicularly to the paper surface and in the direction indicated by the arrow 12 in the drawing is disposed such that the lowermost portion 16 of the roller 14 underlies an ink liquid level 18, i.e., a part of the roller 14 is constantly immersed in the ink 6. On the side portion of the roller 14, a regulating blade 20 composed of a plate-like elastic member is provided fixedly. The regulating blade 20 protrudes generally tangentially to the roller 14 and downstream in the direction of rotation of the roller 14 to be in contact with the roller 14. Another roller 22 is provided over the roller 14 in a contact relationship with the roller 14. On the side portion of the roller 14, there is further provided a removing blade 28 in a contact relationship with the roller 14 at a position downstream of a contact portion 24 with the regulating blade 20 and a contact portion 26 with the other roller 22 in the direction of rotation of the roller 14. The removing blade 28 is formed of a single plate-like elastic member and directed generally tangentially to the roller 14 and upstream of the roller 14 in the direction of rotation of the roller 14.
Next, a description will be given to the operation of the ink supplier 2 with reference to FIG. 10. The ink 6 adhering to the surface of the roller 14 below the ink liquid level 18 is pumped up with the rotation of the roller 14 to reach a tip portion 24 of the regulating blade 20. The ink 6 receives a given pressure from the tip portion 24 of the regulating blade 20, whereby the surplus ink 6 is scraped off and removed by the regulating blade 20 and a thin layer of the ink 6 having a desired uniform film thickness in accordance with the tip pressure of the regulating blade 20 is formed on the surface of the roller 14. Thereafter, the tin-film ink 6 is transferred, i.e., supplied to the surface of the other roller 22 rotating in the opposite direction (rotation indicated by the arrow 32) to the roller 14, while keeping contact with the roller 14, at the contact portion (supply position) 26. After that, the ink 6 remaining on the surface of the roller 14 reaches the tip portion 30 of the removing blade 28. Since the tip portion 30 of the removing blade 28 is in contact with the roller 14, while being oriented in such a direction (direction indicated by the arrow 12) as to collide with the direction of rotation of the roller 14, the remaining ink 6 is scraped off by the tip portion 30 to return into the container 4. Accordingly, the ink 6 does not remain on the surface of the roller 14 after it has passed through the tip portion 30 of the removing blade 28.
The refreshed surface of the roller 14 from which the remaining ink 6 has been scraped is immersed again in the liquid ink 6 by the rotating operation of the roller 14 to be prepared for another transfer to the roller 22, i.e., another ink supply. In the ink supplier 2 with the conventional structure, therefore, the thin layer of the ink 6 is constantly formed on the surface portion of the roller 14 lying between the position 36 at which the roller 14 emerges from the ink liquid level and the position at which the surface of the roller 14 comes in contact with the tip portion 30 of the removing blade 28 regardless of whether an ink supply operation is being performed or halted. This particularly presents a problem when the time interval between the halting of the ink supply operation and the initiation of the subsequent ink supply operation is long. This is because the layer of the ink 6 dries during the long period of time and tends to stick to the surface of the roller 14 and there may be cases where an ink supply from the roller 14 to the roller 22 is not effected as desired due to the stuck ink 6 in the subsequent ink supply operations, with the result that a formed image is disturbed.
On the surface portion of the roller 14 lying between the regulating blade 20 and the removing blade 28 in the direction of rotation of the roller 14, the ink is thinly spread out to have a large contact area with an outer atmosphere so that such drying is especially likely to occur.